pOH Calculator
Find the pOH and pH of a solution from its hydroxide-ion concentration, or convert between pH and pOH.
How it works
pOH = −log₁₀[OH⁻] · pH = 14 − pOH · [OH⁻] = 10^(−pOH) (25 °C)
pOH mirrors pH but tracks the hydroxide ion: it is the negative base-10 logarithm of the OH⁻ concentration. Because water self-ionises, pH and pOH always add to 14 at 25 °C, so knowing one gives the other instantly. This tool works in either direction — from a hydroxide concentration to pOH and pH, or between pH and pOH.
Worked example
A solution with [OH⁻] = 0.001 = 10⁻³ mol/L has pOH = −log₁₀(10⁻³) = 3, and therefore pH = 14 − 3 = 11 — a basic solution.
Sources: Self-ionization of water — Wikipedia
Frequently asked questions
How are pH and pOH related?
At 25 °C they always sum to 14, because the ion product of water Kw = [H⁺][OH⁻] = 10⁻¹⁴. Add pH and pOH and you get 14; subtract either from 14 to find the other.
When is pOH more convenient than pH?
For basic solutions, where you often know the hydroxide concentration directly — for example from a strong base like NaOH. Computing pOH first and subtracting from 14 avoids an extra step.
Does the sum stay 14 at other temperatures?
Not exactly. Kw changes with temperature, so the pH + pOH total shifts slightly away from 14 when the solution is not at 25 °C. The 14 figure is the standard room-temperature value.
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